The present invention relates to a pressure control valve for controlling a pressure of a fluid substance to be fed through a fluid passage or channel. Also, the present invention relates to a pressure control valve preferably for use with an automobile brake system, for example.
Recently, a fluid pressure control system for controlling a pressure of an operating or working fluid into a predetermined value, in particular for use in an automobile brake station tends to employ a power driven pressure-source in order to provide a highly precise operational control to the automobile. Another system with an accumulator in the pressure source may be required according to a content of the control.
Specifically, for the pressure control valve system mounted in a connection between the pressure source and wheel cylinder, a highly precise pressure control is required for the wheel cylinder. For this purpose, a proportional pressure control valve system capable of controlling the fluid pressure in a precise manner according to an electric instruction tends to be employed instead of the conventional, simple switching or shutdown valves.
A majority of the conventional proportional pressure control valves employs an electromagnetic spool valve in which a spool or piston is moved to change fluid passages and/or control the open ratio of the passage. Disadvantageously, sensitive spools can move back and forth along its longitudinal direction excessively to cause vibrations. To overcome this problem and then to attain a steady-state spool valve, an improved spool valve with an orifice that defines,a fluid chamber together with the end portion of the spool is proposed in the Japanese Patent Unexamined Laid-Open; Publication JP(A) No. 4-125374, for example.
Referring to FIG. 5, there is shown a conventional proportional pressure control valve generally indicated by reference numeral 100. The pressure-control valve 100 has a housing 101 with an elongated piston chamber 102 formed therein and extending vertically. The piston chamber 102 receives a piston or spool 103 therein so that the spool 103 is guided by the piston chamber 102 to move ups and downs. The housing 101 has four ports 104-107 each connected with the piston chamber 102. Also, the housing 101 includes upper and lower fluid chambers 108 and 109 adjacent to the opposite, top and bottom end portions of the spool 103, respectively. On the other hand, the spool 103 has an axial passage 110 extending from its top end positioned adjacent to the upper chamber 108. In the vicinity of an open top end of the passage 110, the spool 103 has a partition with a small hole or orifice 111 that connects between interior and exterior of the passage 110. The spool 103 also has transverse holes 112 adjacent to the lower fluid chamber 109 so that the passage 110 is connected with the lower fluid chamber 109 through the holes 112. Further, the spool 103 is formed in its outer peripheral surface with upper and lower passages 113 and 114. The spool 103 so constructed is forced upward by a bias spring 115 and, a connecting mechanism 116 for the mechanical connection between the spool 103 and bias spring 115, so that it sakes an elevated position (not shown) in the housing 101.
With the arrangement, a fluid substance such as pressurized oil is supplied into the port 105. Thee fluid flows through the lower fluid chamber 109, transverse holes 112 and then fluid passage 110 into the upper fluid chamber 108. As a result, the fluid pressure applies on the top surface of the piston 103. This causes the spool 103 to move a downward direction into a lowered position shown in FIG. 5, which in turn allows the ports 106 and 107 to be connected to one another through the peripheral pass age 114.
The operating fluid is then drawn from the port 104. In this instance, the operating fluid is transported from the upper fluid chamber 108, passage 110, transverse hole 112 and lower fluid chamber 109 and then discharged from the port 104, which causes the spool 103 to move upward. As a result, the passage 114 is closed and, on the other hand, another passage 113 is opened to connect between ports 106 and 107.
The flow of the operating fluid between the fluid passage 110 and the upper fluid chamber 108 is restricted at the orifice 111, which prevents a rapid translation of the spool 103. This ensures a steady-state movement of the spool 103. Also, by adjusting the size of the orifice 111, the translation velocity of the spool 103 can be changed.
Disadvantageously, the proportional pressure-control valve system so constructed may hold air or bubbles in the fluid chambers which would cause vibrations of the spool. Typically, for removing bubbles from the upper fluid chamber 108, the operating fluid within the housing 101 may be drawn through the ports and then exchanged with another operating fluid. However, such operation for removing bubbles can be done only when the valve system is out of operation and requires additional and complicated operations. Also, the removed bubbles may be fed back into the passages or chambers at the downward movement of the spool.
Accordingly, a pressure control valve of the present invention has housing and a piston member. The piston member is housed in the housing so that it moves between first and second positions. The housing includes a piston chamber for guiding the piston member between first and second positions while keeping a sealing engagement with the piston chamber. First and second chambers are positioned adjacent to opposite ends of the piston member so that volumes of first and second chambers are changed depending upon a movement of the piston member. First and second ports are connected when the piston member takes the first position but disconnected when the piston member takes the second position. Third port is connected with the first and second chambers but disconnected from the first and second ports when the piston member takes the first position but connected with the second port when the piston member takes the second position. A partition is defined between the first and second chambers. Also, the partition has an orifice for connecting between the first chamber and the third port.